Apparatus for deoiling wax



J1me 1965 R. E. SPARKS ETAL 3,192,125

APPARATUS FOR DEOILING WAX Filed Aug. 1, 1961 2 Sheets-Sheet l T i T Ton. STRIPPER 26 IO"- WAXY T T was 23 a l8 l2 9 l (hi- FLASH,

DRUM v a FILTER 24 on. PRODUCT WAX -s- ,-2O STRIPPER WAX 22 FIGURE IPRODUCT ROBERT E. SPARKS INVENTORS STEPHEN F. PERRY BY W H.

PATENT ATTORNEY J n 1965 R. E. SPARKS ETAL 3,192,125

APPARATUS FOR DEOILING WAX Filed Aug. 1, 1961 2 Sheets-Sheet 2 3|PRESPRAYED 35 SPHERES |L+SOLVENT FINES 43 42 as 280,0 s u a 60 31 60 asSOLVENT 37 3' a K o 2800 0 25 so rs I00 I25 EXTRACTION TIME, MINUTESFIGURE 5 FIGURE 4 ROBERT E. SPARKS INVENTORS STEPHEN E PERRY BY W PATENT ATTORNEY United States Patent 3,192,125 APPARATUS FOR DEOILING WAXRobert E. Sparks and Stephen F. Perry, both of Westfield,

NJ., assignors to Esso Research and Engineering Company, a corporationof Delaware Filed Aug. 1, 1961, Ser. No. 128,522 8 Claims. (Cl. 19614.5)

This invention relates to improvements in the art of dewaxing ofpetroleum oil fractions. This invention is particularly concerned withan improved process for dewaxing lubricating oil fractions. Inaccordance with the invention, a waxy oil feed is sprayed in the form ofsmall droplets which solidify by direct contact with a cold fluid,followed by extraction of the oil from the solidified droplets with anappropriate solvent. An advantage of the invention is that thesolidified wax droplets are easily separated from the dewaxed oilproduct.

Petroleum oil fractions obtained from parafiinic crudes contain variousamounts of wax. This is particularly true of lubricating oil fractions.In order to obtain lubricating oils which will flow at low operatingtemperatures, i.e., have low cloud and pour points, it is necessary toremove from the lubricating oil stock the wax present. The wax recoveredin dewaxing parafiinic lube oil stocks is itself a valuable product.

There are several commercial solvent dewaxing processes now in use. Thetwo most widely known are propane dewaxing and ketone dewaxing. Inpropane dewaxing, the waxy oil is mixed continuously with liquid propaneunder pressure and charged alternatively to two batch chillers. The rateat which the propane waxy oil mixture is cooled is critical. If themixture is cooled too rapidly, shock chilling results causing the wax toform as fine particles which are ditficult to filter. The chillers areused alternatively; while one is chilling a charge of waxy oil, theother is being cleaned and emptied. The contents of the chillers arethen filtered. In order to produce dewaxed oil with a pour point of15-20 F., it is necessary to dewax with propane at 25 to -35 F. Innormal operations, the filter cloth used to filter the dewaxed oil froma precipitated wax gradually blinds or becomes clogged and requires aperiodic hot wash with a solvent, such as kerosene, at intervals ofabout 4 hours or so.

In ketone dewaxing, a mixture of MEK and toluene is generally used asthe solvent. In this process, the waxy oil is mixed with the ketonesolvent and charged to double-pipe scraped surface heat exchangers andthen to chillers of similar construction wherein the mixture is chilledcontinuously to the desired filtering temperature. On chilling, the waxyoil-solvent mixture precipitates the wax and a slurry is formed.v Thecooled wax slurry is then charged to a rotary filter wherethe wax isseparated from the dewaxed oil and solvent. A filtering temperature ofabout 0 to 10 F. is required to produce a dewaxed oil of 15-20 F, pour.

Another method of dewaxing oils which has been tried is to feed the waxyoil directly into a cold solvent; (i.e. at a point beneath the surfaceof the solvent or just above the surface), such as liquid propane, toprecipitate the wax and to extract the oil from the solid wax particle.In accordance with this process, coarse, flake-like crystals are formedwhich are easily broken and which make fines, which are difiicult tofilter. The size of the crystals were relatively large, and theextraction of oil from the crystals was not efficient. More recently, aprocess has been developed for separating small amounts of oil fromcrude parafiin waxes; i.e., a decoiling process. It has been reportedthat, in accordance with this process, a crude pet rolatum waxcontaining 25% oil is sprayed into a vessel containing a cooling gas.The cooling gas will solidify the petrolatum if the oil content is lowenough. The

3192325 Patented June 29, 1965 cooled solid grains of wax are collectedat the bottom of the vessel and are scraped off and subsequently treatedin a separate vessel with a deoiling solvent. The resulting mixture mustbe centrifuged or filtered to separate the wax from the oil and solvent.This process has proved inefiicient and ineffective in separating waxfrom waxy oil feeds which contain large amounts of oil. When waxy oilfeeds containing large amounts of oil or more than about 30% are sprayedin accordance with that process, they are only partially solidified inthe cold gas present and form agglomerates which stick together in thebottom of the vessel. In this condition, they cannot easily be scrapedout of the vessel nor can they be effectively deoiled and filtered.Further, this process is not operative in removing oil from residualsstocks regardless of oil content, since these stocks contain highmolecular weight waxes which do not solidify and form stickagglomerates.

The prior art processes have not provided an economical, efiicient, orcontinuous method of dewaxing high oilcontent waxy oil fractions thatproduces a wax that can be easily deoiled, and effectively filtered orcentrifuged, or otherwise separated from the dewaxed oil. The propaneand ketone dewaxing processes require a considerable investment inequipment. The propane process is not a continuous process, but rather abatch or semi-continuous process. The ketone process requires a largeinvestment in complicated scraped-surface exchangers and both processesrequire well-controlled chilling rates. Both processes require largeinvestments in rotary filtration equipment to remove the small waxcrystals. Neither process produces the wax material in a form which isreadily filtered, and in which the oil can be readily separated from thewax material. The spray deoiling process is not efiective in that theoil in high oil-content feeds cannot be separated from wax in thismanner, and the process requires in addition a filtration orcentrifugation step.

It is an object of this invention to provide an improved process forseparating wax from waxy oil fractions which is efiicient andeconomical. It is another object of this invention to provide acontinuous process for separating wax from lube oil fractions, whichresults in a wax which is easily filtered or separated from the dewaxedoil. A further object of this invention is to provide a process ofseparating Wax from waxy lube oil fractions which results in a highdewaxed oil yield, and a wax and dewaxed oil which are easily separated.

In accordance with a preferred embodiment of this invention, a waxypetroleum oil fraction is heated to a temperature slightly above itspour point and charged to a cooling tower or vessel through anatomization device to give droplets of waxy oil of a critical size toprovide maximum extraction rate of the oil, as well as allowing asimplified method of separating the resulting solidified wax dropletsfrom the oil-solvent solution. The waxy droplets are cooled bycontacting them with cold vapor which cools the droplets sufficiently tocrystallize enough of the wax in the droplets so that when the dropletscontact the liquid deoiling solvent at the bottom of the tower, they arein spherical shape, which shape is not greatly deformed on contactingthe liquid solvent. The remainder of the wax present in the droplet issolidified while in contact with liquid solvent while descending to thebottom of the vessel. As the wax in the droplet solidifies in the liquidsolvent, the major portion of the oil present in the wax droplet isextracted. At the bottom of the tower wax droplets which aresubstantially reduced in oil content are collected. Fresh liquid solventis introduced at one or more points in the tower and removed at the topof the liquid layer, together with the extracted oil. The supernatantliquid may contain a small amount of wax fines which may be readilyfiltered or centrifuged. The wax at the bottom of the tower may beremoved from the bottom of the vessel and taken and stripped of anyexcess solvent. For most ope-rations, the separation is good enough thatthe bulk of the wax does not have to be filtered or centrifuged toremove oil. The solvent is removed by flashing it off from the wax. Thetemperature of the liquid solvent is warm enough to extract the desiredamount of oil from the wax droplets, but not sufiiciently warm todissolve an appreciable amount of wax from the droplets. The solventwill be sufiiciently cold to solidify any liquid wax remaining in thedroplet.

When the above process is carried out in a liquid solvent having adensity lower than that of the feed, the extraction takes place whilethe solidified feed droplets are descending countercurrently through theliquid. If proper internal apparatus is inserted in the extractiontower, well-controlled countercurrent motion of solid particles andliquid can be obtained. This renders'the process especially economical,since many countercurrent equilibrium extraction stages can be obtainedin the tower, requiring less solvent for extraction of a given oil yieldthan would be required for simply mixing the solids with the solvent.The amount of oil extracted from the solid droplets can be closelycontrolled by the number'of equilibrium stages obtained and the volumeof solvent employed.

Our process, has several advantages over the known processes of dewaxinglubricating oil stocks; namely the equipmentrequired is much simpler andmuch less expensive, the process obtained is continuous, the waxdroplets obtained are more easily separated from the dewaxed oil, andthe holdup time or residence time of the droplets in the dewaxing vesselis favorable. The wax droplets formed are of aproximately sphericalshape and sufficiently hard by the time the oil is removed and they donot agglomerate or cake, and therefore allow the solvent and dewaxed oilto be easily separated from them.

The nature and objects of the invention will be better understood whenreference is made to the accompanying drawings in which:

FIGURE 1 is a flow plan of a preferred embodiment of our dewaxing plant.

FIGURE 2 is a detailed drawing of the internal structuer of the deoilingzone.

FIGURE 3 shows a top view the extraction column..

FIGURE 4 shows a top View of a left horizontal baffle used in theextraction tower.

FIGURE 5 shows the effect of droplet diameter and extraction time on oilyield.

The waxy petroleum oil fractions which may be used in accordance withour process usually boil above 460 F. Pour points of the feed stocks aregenerally above 30 F. Petroleum stocks having a wax content of fromabout 5 to 98% by weight wax can be dewaxed in accordance with thisinvention. Preferably distillate and residual lube oil stocks havingabout a 12 to 25% by weight wax and boiling in the range above 525 F.and having a pour point of about 90 F.-140 F. are treated.

The cooling gases used to initially cool the waxy oil droplet formingthe sphere may be light hydrocarbons, such as methane, ethane, propane,and butane, or air, ammonia, nitrogen dioxide, carbon dioxide, S0Freons, and the like. Propane vapor, however, is preferred. Propane hasan advantage of being an autorefrigerant as well as a solvent. The waxyoil droplet is contacted with the cool gaseous vapor and forms a sphereof sufficient hardness so that when the droplet contacts the liquidoil-extracting solvent near the bottom of the vessel, it is notappreciably deformed. The temperature of the cooling vapor will be belowthe pour point of the waxy oil feed. Generally, temperatures of -l6 2 to'-}-100 F. can be used. The time that the waxy oil droplet is present inthe gaseous cooling vapor will be a matter of the paddles used in of afew seconds. This is the time that it takes the droplet to fall from thespray nozzle to the surface of the liquid cooling solvent. The height ofthe gaseous cooling column, and the temperature of the cooling gas willbe determined by the temperature of oil feed and its wax content. Thedilference in the temperature between the feed and the cooling gas willbe regulated so that about to W of the B.t.u.s which are necessary tocompletely solidify the wax in the droplet will be transferred to thegaseous cooling vapor in the time that it takes the droplet to fall fromthe spray nozzle to the surface of the liquid cooling solvent. Theremaining B.t.u.s which must be transferred to completely solidify thewax in the droplet will be absorbed by the liquid cooling solvent.

In-a preferred embodiment,liquid propane functions as the coolingliquid, as well as the oil-extracting solvent, and as the source of coldvapor. The volume throughput of the cooling vapor will be determined bythe throughput of waxy oil feed and the desired amount of cooling in thevapor space. The amount of cooling vapor employed may be easilyregulated within wide limits by removing part of the vapor before itcools the droplets or by adding more vapor if desired.

In another embodiment of the invention, instead of using a cooling gasto form the initial uniform spheres of waxy oil droplets, liquids whichare poor solvents or antisolvents for waxy oil may be used. Suchmaterials are liquid ammonia, .methanol, water, aqueous solutions,saturated oil-solvent solutions, and the like. The high interfacialtension between the wax and the nonsolvent forms a sphere, immediatelyon contact of the Waxy oil droplet with the nonsolvent. In thisembodiment, the atomizing nozzle will be only far enough above theliquid surface to allow the droplets to be formed before hitting theliquid. The nonsolvent may be kept in a vessel separate from theextracting solvent.

The deoiling solvent may be selected from liquefied light hydrocarbons,such as ethane, propane, butane, pentane, and hexane; ketones such asMEK, MIBK, and mixtures such as MEX/toluene, MEK/MIBK, and the like. Thedeoiling solvent also functions to complete the cooling of the'waxy oildroplet. About one-half to nine tenths of the solidification or coolingof the droplet takes place in the deoiling solvent. After the waxy oilydroplet has partially solidified in the cooling vapor, it contacts thecooling solvent. Suificient solidification has taken place in the vaporso that when the droplet contacts the cooling solvent, its shape is notappreciably deformed.

In one embodiment of the invention, liquid propane is used as a coolingand deoilingsolvent because of its autorefrigerant characteristics, itslow solubility for wax, and high solubility for oil at low temperatures.When the waxy oil droplet is contacted with liquid propane, the; oil inthe droplet is extracted by the liquid propane. Substantially all theoil present in the droplet may be extracted into thepropane at highdilutions. Liquid propane solvent enters the dewaxing vessel at thebottom of the vessel and is removed at the top of the solvent phase.This effects a countercurrent extraction of theoil from the droplets.The. oil may be so well removed from the droplets that further treatmentof the hardened wax droplets not necessary. After the waxy droplet isremoved from the vessel,.:all that is required is that any excesssolvent present on the, droplets be removed by flashing or stripping.One of the most important advantageous of this process is that nocentrifugation or filtering step is required for removing the oilsaturated solvent from the crystallized wax droplet. The solvent,however, may also be removed by centrifuging or filtering. The uniformspherical shape of the droplets, and the fact that they are not deformedand are allowed to form almost perfect spheres, allows easy separationand flow of the solvent around each of the droplets. The wax inspherical shape also has less tendency to break into small particleswhich would be difiicult to separate from the solvent. The droplets donot cake or agglomerate and subsequent filtration or centrifuging, ifdesired, is relatively simple.

The temperature of the extracting solvent, for example, propane, isdependent upon the pour point of the desired dewaxed oil, and thecontent of the wax in the waxy oil droplets. Solvent temperatures of-162 to +100 F. may be used. Where liquid propane is used as thesolvent, the dewaxing vessel is maintained at a pressure of about 5 to20 p.s.i.g. in order to keep substantially all of the solvent in theliquid phase. Autorefrigeration is effected, however, by partiallyvaporizing a portion of the solvent, thereby cooling the remainder. Thesolvent that is vaporized is collected, compressed, condensed, andrecycled to the bottom of the vessel. The ratio of solvent to feed forextracting of about 1/1 to /1 can be used. The ratio of solvent to feedis dependent upon the desired pour point of the resulting oil, the waxcontent of the feed, :and the amount of oil desired to be extracted. Thedilution and, hence, the flow rate of solvent will determine, to acertain extent, the holdup time or residence time of the waxy oildroplets in the dewaxing vessel. The residence time of the waxy oildroplets in the deoiling solvent is between 5 minutes and 10 hours.Naturally, the shorter the residence time, the higher, throughput andthe greater the dewaxing capacity of the vessel. Depending on thecharacteristics of the waxy oil feed, residence time selected will besuch that it is sufficient to extract substantially all of the oilpresent.

The droplet size of the atomized waxy oil feed in this invention iscritical. The physical form of the droplet when it contacts the liquiddeoiling solvent is also critical. Flake-like crystals, though easy toextract oil from, are difficult to handle and almost impossible tofilter. The slightest agitation causes them to break into fines, whichmake filtration and subsequent handling very difficult. Droplets ofuniform spherical shape are preferred. Once these droplets harden, thereare areas between the droplets for solvent to go through and extract theoil. This also provides for ease of separation of dewaxed oil andsolvent from the wax droplets. Wax droplets of large size, however, areundesirable because it takes an exceptionally long time to extractsubstantially all of the oil from these droplets, as shown in FIGURE 5.This would require an excessively long holdup time and lower thecapacity of a given dewaxing vessel. On the other hand, exceptionallysmall droplets are also undesirable as they decrease settling rate, andtend to pack closely and/or entrain overhead causing the filtration andseparation of the dewaxed oil and solvent from the droplets to bedifiicult. Narrow size distribution spheres are preferred for ease ofhandling and uniformity of extraction. Droplets of fairly wide sizedistribution, such as obtained from conventional spray nozzles can,however, be used.

Waxy oil droplets of a diameter at 50% cumulative volume referred to asvolume median, of between 20- 5000 microns can be used. However, spheresof 300- 1000 microns are preferred, though diameters of 100- 2500 canalso be used. As previously stated, the size of these waxy oil spheresis critical. Not only is the size a critical, but the physical shape ofthe droplet is also critical. By contacting the waxy oil droplet with acooling gas, as stated above, such as propane, the droplet is allowed toform a spherical particle and allowed to become sufficiently hard sothat, when the sphere contacts the liquid extracting solvent, it is notappreciably deformed and enters the extracting solvent in approximatelyspherical shape. In this state, the oil is easily extracted from thesphere, and the droplet solidifies in the shape of a sphere. When thesespheres stack or collect at a stage or in the bottom of the dewaxingvessel, there are interstices or spaces between the droplets betweenwhich the extracting solvent may flow. In this manner, substantially allof the oil is removed from the droplets efiiciently and elfectively in arelatively short time. This manner of treating the waxy oil dropletsalso obviates the necessity of filtering dewaxed oil and solvent fromthe bulk of the waxy oil droplets, since substantially all of the oiland solvent solution is removed in this manner and the wax patricles areseparated simply by settling. The wax droplets are then withdrawn fromthe bottom of the vessel through a gear or screw pump and any excesssolvent stripped from the wax.

The temperature at which the dewaxing, cooling, and extraction iscarried out will, of course, depend upon the temperature of the feed andupon the pour point of the dewaxed oil desired. Temperatures of coolingvapor of 162 to F. can be used. However, temperatures of the coolingvapor of -35 to +40 F. are preferred.

The temperature of the cooling solvent will depend to a certain degreeon the temperature of the cooling vapor. Where propane is used as acooling and deoiling solvent, temperatures of -35 to 0 F. are preferred.However temperatures of -44 to +40 F., as Well as temperature of 162 to+100 F. can be used. The temperature, of course, is dependent upon theparticular deoiling solvent used.

Pressure in the vessel is generally about atmospheric pressure. However,pressures of 5 to 300 p.s.i.a. can be used, but pressures of 1540p.s.i.a. are preferred. The residence time of the Waxy oil droplet inthe vessel is the time that it takes to fall through the cooling gas orvapor, plus the time in the deoiling solvent. This time in the deoilingsolvent may be controlled by the rate of flow of propanecountercurrently through the droplets and by constructing bafi'les orstages within the vessel to hold up the droplet. Residence times of 30to 60 minutes are preferred. However, depending upon the oil content ofthe droplet, residence times of 30 minutes to 5 hours, as Well as 5minutes to 10 hours, can also be used. To obtain maximum throughput andmaximum capacity of a given piece of equipment, however, a shorterresidence time for a specific oil yield makes for greater throughput.

The ratio of solvent to feed is, of course, dependent upon theparticular extracting solvent used and the temperature at which the oilis extracted from the droplets. Ratios of U1 to 10/1 can be used.However, a ratio of 1/1 to 5/1 and, specifically, for economic reasons,a

ratio of 1/1 to 3/1 are used. The fiow rate of the extracting solvent iscountercurrent to the gravity flow of the waxy oil droplet. This rate offiow is naturally contingent upon other variables and should be set aslow as possible to minimize entrainment of fine or small spheres in theoil-solvent stream. The droplet size is determined by the design of thespray nozzle, the pressure drop across the nozzle and the viscosity andsurface tension of the sprayed waxy oil feed.

The temperature at which the waxy oil feed is charged to the dewaxingvessel will be above its pour point. The pour point and viscosity of afeed may be reduced by addition of pour point inhibitors and/or solventsfor the oil, and/or light hydrocarbons. In view of the variety of feedsthat may be used and the wax content of the feeds, aswell as theviscosity of the feeds, this encompasses feed temperatures of 5 to 360F. The lubricating oil stocks that are to be dewaxed in accordance withthis invention will have feed temperatures of about 40 220 F. The Waxcontent of the feed will vary, depending on its crude source, as well asthe particular cut that is taken. Oil contents as high as 98% by weightcan be handled. However, it would be more common to have waxconcentrations in the stock of l0-65%. Where the lubricating oil stocksare used, wax concentrations in the nature of 12-25 will be more common.

For a typical 2500 barrel/day rate of throughput of feed, a verticalvessel approximately 10-80 feet in height and 8-25 feet in diameter canbe used. The height of the cooling gas column can be 5-40 feet; wheras,the height of the cooling solvent may be 570 feet. The

, height of either of these two columns may be easily regulated and willdepend upon the type of feed that is being treated, the coolants used,and the internal apparatus in the tower.

In a preferred embodiment of the invention, propane vapor is used over aliquid propane cleoiling and cooling solvent. The dewaxing is carriedout at about atmospheric pressure, and the vessel is maintained at atemperature of about 30 F. This temperature is attained by vaporizingpart of the propane liquid, thus cooling the remainder. This is anautorefrigerated process. Where MEK-toluene is used as the extractingsolvent, the MEK-toluene is generally cooled externally. This may bedone through heat exchange with propane or ammonia refrigerants. Inanother embodiment of the invention, a nonsolvent or antisolvent for thewax may be used to form the uniform spherical shaped droplets. In suchcase, two vessels may be used; one of them to form the droplets, and theother to deoil the droplets.

An understanding of various aspects of the invention may be aided byreferring to the accompanying drawings and the discussion thereof. Thedrawings show arrangements of apparatus which can be used in thepractice of an embodiment of the invention. It will be readilyappreciated that these drawings are in the nature of flow diagrams andthat numerous pieces of individual equipent, for purposes ofsimplification, have been omitted.

Referring now to FIGURE 1 of the drawings, a waxy parafiinic lube oilfraction having a pour point of 90 F., a boiling range of 525-850 F. andhaving a viscosity of 4 centistokcs at 210 F. is charged to dewaxingvessel 3 through line 1 and is atomized by spray nozzle 2, forming waxyoil droplets 25 of volume median diameter .300-1000 microns. The lubeoil fraction has a wax content of 10-25% by weight and is fed to vessel3 at a temperature of 40-220 F. The pressure in vessel 3 in the vaporphase 4 is about atmospheric pressure or sufiicicnt to prevent violentboiling of the liquid propane. Vapor space 4 is filled with propanevapor at a temperature of 44 to +40 F. The atomized waxy oil feed oncontacting the cold propane vapor forms spheres of wax and oil andpartially solidifies prior to contact with the liquid propane in thevessel. The waxy droplets contact liquid propane 5, which is at atemperature of 44 to F. The residence time of 30 minutes to 5 hours ofthe droplets in the liquid propane is sufficient for the droplets tocompletely solidify, and the oil in the droplets to be substantiallyextracted. The ratio of solvent to oil is 1/ 1 to 5/1. By means ofbaffies 6 and paddles 7, the droplets descend in a spiral motioncountercurren'tly to the rising propane solvent which enters the vesselthrough line 15, and the holdup time is controlled by the number ofbattles 6, the height of the liquid column and the speed of rotation ofpaddles 7 on shaft 25. The hardened droplets collect at the bottom ofthe dewaxing vessel in cone 28 wherein the fresh liquid pnopane isintroduced and effectively extracts any remaining oil present in thedroplets. The deoiled solidified droplets 26 collect in the bottom ofthe vessel formed by cone 2-8..and are removed from the vessel by gear"or screw pump '8 and through line '9, and are taken to a solventstripper 20 from which any excess propane solvent is removed from thewax. The stripped solvent is recycled to flash drum 13 via lines 21,and12. One of the 'big advantages of my invention is that suflicientseparation of wax, and dewaxed oil and solvent solution is obtained bythe settling action of the droplets which makes it unnecessary tosubsequently centrifuge or filter the wax. The liquid propane coolingand extracting solvent entering through line 15 passes countercurrcntlythrough the hardened wax droplets in cone 2% upwardly in a spiral motionthrough the liquid solvent column 3 and is withdrawn through line 16 andpasses through cartridge filter 1'7. A small amount of wax fines, lessthan about 13% by weight of the total feed is present in the dewaxed oiland propane solution withdrawn .throughline 16. These fines are removedfrom the oil solvent mixture by centrifuge or cartridge filters 17 andare taken via lines 10 and 9 to the wax stripper 20. The dewaxed 'oiland propane sol-vent are removed from cartridge filters 17 byconventional meansand are taken via line 18 to an oil stripper where thepropane solvent is stripped from the dewaxed oil. The dewaxed oil isremoved for further treatment and the stripped solvent is recycled topropane compressor 11. Propane vapor is withdrawn from vessel 3 via line10 and is taken to compressor 11 wherein it is compressed and passed viaa condenser, 27 and line 112 to propane flash drum 13. In flash drum 13,the temperature and pressure are controlled so that a sufiicient amountof propane vapor may be withdrawn through lines 14 and 26 and charged tocompress-or 11 and vapor space 4, in vessel'3, to control the coolingtemperature and pressure of the propane vapor in space 4. The remainderof the recycled propane in liquid form from flash drum 13 is withdrawnthrough line 15 and charged'to the bottom of dewaxing vessel 3. The waxremoved from the bottom of vessel 3 is substantially reduced in oilcontent. The dewaxed oil removed through line 18 has a pour point ofabout 20 F.

By controlling the volume median diameter of the waxy oil dropletsatomized from spray nozzle 2 within a critical size range of 3004000 andcontrolling the temperature of the propane vapor, solidification of thedroplet in the vapor is sufficient so that when the droplets strike theliquid propane solvent, they are sufliciently hard that they are neitherdeformed nor broken up. In the propane solvent, the solidification iscompleted and the oil is extracted from the droplets while they passcountercurrently to the propane solvent. Due to the approximatelyspherical shape of the dro lets, as they collect in the bottom of thedewaxing vessel 3 in cone 28, there is sufiicient space between thedrops so that substantially all the oil is removed by the propaneintroduce-d through line 15, and that the wax removed via screw pump 8,and line '9, is substantially free of dewaxed oil and has only to beseparated from the propane deoiling solvent by wax stripper 20. Screwpump 8 is operated in such a manner that most of the interstitialsolvent present in the settled wax solids is squeezed from the waxdroplets and remains in the column, while the wax substantially free ofsolvent and bills pumped out. This combination of steps is critical inobtaining the ease and efficiency of the separation of wax from waxy oilstocks in accordance with my inventive process.

In FIGURE 2 of the drawings is shown a staged extraction zone which maybe used intone embodiment of my invention. This apparatus was used todeoil a waxy lube stock containing 87.5% by weight oil (as measured bythe ASTM oil content procedure with secondary butyl acetate at 0 F). Inthis embodiment, the droplets of waxy lube stock were preparedexternally from the toil extraction zone.- The lube stock used had apour point of F. and a cloud point of F. and a kinematic viscosity of 4centistokes at 210 F. The feed was heated to 220 F. and sprayed througha swirltype pressure nozzle. The spray droplets were received inmethanol at temperatures between +15 and +45 F. The distance of thesurface of the methanol from the nozzle is not critical, when using anantisolvent to form the spheres, and in this instance was about 1 8inches. The spray droplets had a wide size distribution and a mediandiameter of approximately 500 micnons. The droplets were spherical inshape and showed no tendency to agglcmerate or to stick to metal orglass surfaces. The droplets were cooled to the desired extractiontemperature of 20 F. in cold methanol, then separated from the coldmethanol by filtration and subsequently washed with methylethylketoneand then hexane.

Instead of solidifying the drops in methanol they may, as has 'beenpreviously described, be .solidified by falling through cold propanevapor. A similar spray distribution of the same feed stock, as wasdiscussed immediately above, was allowed to fall feet through a risingstream of propane vapor at a temperature of 0 to F. After falling thisdistance through the propane, the sprayed droplets fell into a body ofhexane at 20 to 40 F. Upon entering the solvent, the droplets hadsolidified sufficiently to remain as separate spherical particles.Either of these methods may be used to obtain solidified droplets forextraction with the apparatus described in FIGURE 2.

Now referring to FIGURE 2, waxy oil droplets obtained from the methanolsoldification process were fed through line 31 to the extracting tower33. The droplets contacted the surface 48 of cold hexane deoilingsolvent maintained at a' temperature of 20 F. in the droplet receivingzone 45 at the top of the extraction tower. The droplets were fedintermittently into the top of the tower and fall slowly through zone 45to line 51 in the column where the bed level is maintained. From line 51downward, the bed contains 10-60% solids depending on the throughputrate of solids and liquids. The solids move slowly downward through thecolumn following a spiral path and are removed at the bottom of thecolumn by screw pump 38. Cold hexane solvent is introduced into thecolumn 33 via line 32 and through distribution ring 50 in a downwarddirection and subsequently passes upward through the column in a spiralpath countercurrently to the descending waxy oil droplets. During thecountercurrent contact, the oil in the droplets is extracted by theascending hexane solvent. Wax fines are collected in zone 43 which ismade up by annular baffle 41 and the outside wall of the tower 42 andare Withdrawn with the supernatant solvent through line 44. These finesare separated from the solvent by either centrifugation or filtrationwith I a cartridge filter. Solvent was introduced into the bottom of thecolumn at a ratio of 3.7 to 1 based on the feed rate of waxy oil. Thetakeofl? rate at the bottom of the column was adjusted until the ratioof interstital liquid to bulk sphere vloume was 2.2 to 1. Hence, thetotal volume of liquid rising up the column and being removed at the topwas 1.5 to 1 based on the feed volume. The waxy oil droplets, with asubstantial amount of the oil removed, were collected in the bottom ofthe tower in zone 34 and were compressed in screw pump 38, squeezing outmost of the interstitial solvent present in the settled droplets, whichsolvent remains in column 33, while the deoiled wax is removed throughline 39. The oil content of the wax in this run was reduced from 87.5%to 25%. The dewaxed oil removed by line 44, at the top of the columnafter separation of the wax fines is separated from the hexane solventby distillation. A dewaxed oil yield of 75%, based on feed, Wasobtained. The pour point of the oil obtained from this process was +20F. and the cloud point of the oil was 2 to 6 higher.

Referring again to the apparatus in FIGURE 2, the waxy droplets fromwhich oil is to be extracted is charged through line 31 into zone whichis filled with extraction solvent to level 48. The droplets as theydescend through zone 45 and column 33 are caused to descend in a spiralmotion by alternately contacting horizontal bafiles 36 and by the rotarymotion of vertical paddles 37. Baflles 36 are situated one-half columndiameter apart throughout the height of the column, each bafile havnigthe shape of a half disc (as shown by FIGURE 4) extending halfway acrosthe column. Successive baffles are placed on alternate sides of thecolumn. At the level of each baffle is stiuated a paddle 37approximately one-half column diameter in height and attached to acentral shaft 35 in such a manner that there is only a small clearancebetween the paddle blade, the walls of the columns, and

the bafiles. Each paddle consists of three vertical blades placed apartand each blade having attached to it a short extension 40 of a suitablematerial, such as Teflon, of sufiicient length to touch the wall ofcolumn 33. Each paddle is attached to shaft 35 in such a manner thateach of its blades is in the same vertical plane of the correspondingblades of the paddles above and below it. A mechanical drive, not shown,is attached to central shaft 35 allowing it to be driven over a widerange of rotational speeds. In this manner, all of the paddles arerotated at the same speed. By this arrangement of internals, for aportion of the time during which a droplet is on a bafile 36, it isisolated from two-thirds of the cross-section of the column at thatpoint. The portion of the fluid solid mixture in which it exists isbounded by two of the half baffles 36 and on each side by four blades 37of two paddles, the blades being aligned one above the other. In thismanner, each particle of solids is isolated for a portion of each paddlerevolution from that part of the column at which there is upfiowingsolvent. This isolated portion can be considered as a mixer and settler.It is evident that by controlling paddle rpm. and bafiie distance andsolid and liquid throughput rates, that a wide range of throughputs,dilution ratios and residence times can be obtained.

The above described apparatus overcomes many of the problems associatedwith countercurrent extraction of solids with light solvents. One of theproblems encountered is large scale vertical channeling. Channelingoccurs when solvent introduced in the bottom of the tower moves upwardand the solids introduced in the top of the tower move downward inchannels and bypass each other rather than countercurrently contactingeach other. This particular apparatus allows positive control inprocesses where the density of the entering olvent is less than that ofthe component being extracted from the solid. Further, in a situationsuch as this, where the density of the liquid phase increases with thedistance it moves up the column, due to the presence of increasingamounts of extracted oil, control of the liquid stream and solids, andcountercurrent motion becomes quie difficult. The tower internalsdescribed in FIG. 2 eliminate the strong channeling tendencies in such acolumn, and permit controlled countercurrent motion. If an upward movingchannel of solvent tends to form in one compartment, proper adjustmentof the rotational speed of the paddles will allow this developingchannel to be moved under the next baifie above it so that it cannotpropagate upward, since all the paddles are turning in the samedirection and the entire extraction bed turns. In this manner, allchanneling having a scale larger than the distance between two bafileson the same side of the column can be eliminated, in order to obtain aneflicient countercurrent extraction operation, channeling must beeliminated.

Another problem associated with extraction of liquids from solids is thepoor distribution of the entering liquid at the bottom of the column.Generally, in fluidized bed systems, there exists above the fluiddistributor localized areas in which dilute phase fiuidization occurswith downflow of packed solids between the areas of fiuidization. Thisphenomena tends to decrease countercurrency and the efiiciency of theextraction. The phenomena is eliminated by the apparatus used in thisembodiment of the invention since, when the paddles turn, the entire bedof solids rotates and this phenomena is eliminated. Fluidization of thesolids is also minimized by injecting the deoiling solvent through anannular ring with openings polinited downward rather than upward intothe packed s01 s.

Still another problem associated with countercurrent extraction of solidparticles of wide size distribution is the different rate at which theparticles of difierent size descend through the ascending solvent. Theheavier particles, of course, would move through the column too rapidlyto have the oil contained therein removed. The

1 l apparatus described in FIGURE 2 allows control of the residence timeof the heavy particles. In a column without internals, the largestparticles fall rapidly through the column being extracted only slightly.In the present apparatus, these heavy particles would fall onto a baflle36 and could fall no further until swept off the bafile by slow-movingpaddle 37. Therefore, the minimum residence time for any droplet in atower having the internals shown in FIGURE 2 would be equal to theproduct of the number of the baffies in the column, and the timerequired for a paddle to describe one-half revolution. The apparatussimilarly restricts the maximum rising velocity of any entering freshsolvent which may have a tendency to bypass or channel. The rotationalspeed of the paddles and the geometry of the system therefore givepositive control over the speed of movement of both the liquid and thesprayed solids through the extraction column. The paddles may be rotatedat speeds between & to rpm; preferably at speeds of A to 2 rpm.

There are several variations of this apparatus which will appear to oneskilled in the art. There may be more or fewer horizontal baffles usedand the baffles may be other than half-moon in shape; e.g. pie-shaped,extend more or less than half way across the column. They may be more orless than a half diameter apart. There maybe more than three paddlesattached to the shaft at anyone pint, for example 2 to 6, andconsequently the angle between the paddles may be other than 120. Theheight of the paddles need not be that of the distance between twohorizontal .bafiles. The paddles may be slanted to the horizontalinstead of normal to them, and the horizontal baflies may be slanted tothe horizontal or conical in shape rather than forming a plane.

secondary butyl acetate at 0 F.) is charged to the vessel at atemperature of 160 F. having a vapor pressure in the vessel of 19p.s.i.a.- The waxy oil feed is sprayed through a nozzle into the coolingvapor of propane which is at a temperature of F. The nozzle atomizes thewaxy oil feed resulting in droplets of wide size distribution having avolume median diameter of 400 microns. About one-third of the B.t.u.srequired to solidify all the wax present in the droplets is absorbed bythe cooling propane vapor. Sufficient solidification occurs so that Whenthe droplethits the liquid propane filling the bottom half of the tower,the droplets physical shape is not appreciably deformed. The liquidpropane which is used to complete cooling of the droplet, as well as toextract the oil present, is at a temperature of 35 F. The liquid propaneabsorbs sufficient B.t.u.s from the partially solidified oil droplet tocompletely solidify the droplet. The droplet passes from the top of theliquid propane solvent to the bottom of the solvent in a countercurrentmotion as the oil is extracted from the droplet. The residence time ofthe waxy oil droplet in the liquid propane is about minutes. A dewaxedoil yield of is obtained having a pour point of 20 F.

Our invention is fairly exemplified by the following data:

Table I shows that the content of the oil in the waxy oil feed iscritical, as well as the degree of cooling the droplet attained. It canbe readily seen from the data below that waxy oil feeds having a largeamount of oil present, which are not sufficiently cooked in a gaseousvapor prior to contacting the bottom of the spray vessel, form spongyagglomerates which are difficult to transport and filter and otherwise(1111101111; to handle.

TABLE I Deoilirig tower does not work on high oil content or residualstocks Oil content Approx. Condition of drops Condition of drops onStock (percent by diameter Cooling vapor Distance hitting solid surfacefalling into liquid 131; at (microns) and temp F.) of fall (ft.) nearbottom of column solvent Paraffin lube 87. 5 1, 300 Air (45) 18 Nosolidification Do 87.5 450 Air (520) 14 Particles stick Singleparticles. No

together. sticking or agglomeration. Do 87. 5 280 Propane (535) 12 .doDo. Residual lube stock.-. 58 280 do 12 Particles very sticky Do. Middledistillate 90 280 do 12 Particles soft, partial- Do.

1y agglomerated.

Our invention is further exemplified by the following example: 55 Inorder to show the operability of the present inven- In accordance with apreferred embodiment of this invention, a typical 5,000 barrel a dayfeed rate dewaxing plant is used. The waxy lubricating oil fractionhaving a 90- F. pour point and a waxcontent of 12.5% (by tion in formingdroplets in a non-solvent, feeds containing various amounts of oil weresprayed into cold methanol and then the oil was extracted with varioussolvents. The results are given below in Table II.

TABLE II Process operability on stocks having wide range of oil contentsData for batch extraction of sprayed droplets of wide size distributionhaving median diameters of approximately 400 microns [Drops solidifiedby spraying into methanol] Oil content Filter rate (percent byExtraction Oil (gal. dcwaxcd Stock sccondary- Solvent Dilutiontemperature yield (oil) (hm-Ft?) butyl ratio F.) (percent) for 40%filter acetate at submergencc Residual petrolatum 29. 6 50 M EK/50toluene 3. 0/1 45 42. 8 4. 26 Medium parafl'lnic lube 87. 5 Hexane 2.0/1 20 74. 0 21. 7 Middle distillate 90 MEK/15 methanol 1. 5/1 0 94. 915. 8

The droplet diameter also has a direct effect on the time it takes toextract the oil present in the droplet and the percent of oil yieldobtained. Data were obtained with waxy oil droplets having a median meandiameter of 2800, 910, and 600 microns, using MEK as the deoilingsolvent at a temperature of 35 to 40 F. with a solvent to feed ratio of4/ 1. A run was also made with 280 micron diameter droplets using a50/50 MEK/ toluene deoiling solvent at a solvent to feed ratio of 2/1.In this run, 20% by volume of the deoiling solvent was added to the feedbefore spraying the feed. The data obtained is presented graphically inFIGURE 5 .of the drawings. It can be seen from the drawing that thelarger droplets take a longer time to extract a specific amount of oil.

From the above examples and data, it is evdient that the droplet size,the degree of cooling of the droplet, prior to striking a liquid orsolid surface, and the physical shape of the wax droplets are criticalas related to the efiiciency of filtering and/ or centrifuging theresulting dewaxed oil, and the rate of extracting the oil from thedroplet.

The scope of this invention is not to be limited by the specificexamples and the embodiments herein presented and described, but islimited only by the claims appended hereto.

What is claimed is:

1. Apparatus for removing oil from waxy oil droplets which comprises incombination: (a) a vertical cylindrical vessel, (b) means forintroducing waxy oil into said vessel, (c) means for introducing solventinto said vessel, (d) a plurality of spaced bafiles on alternate sidesof said vessel throughout its height, said bafiles extending less thanall the way across said vessel, (f) a plurality of paddles connected toa central shaft and located between each set of two baffles, saidpaddles having three blades, the blades being spaced approximatelyequidistant apart, the outer edge of said blades being in constantcontact with the interior walls of said vessel and the lower edge ofeach blade being located so as to make continuous contact with thebafile immediately below it.

2. The apparatus of claim 1 wherein each blade has a resilient tip onits outer edge, said resilient tip making a continuous contact with theinterior wall of said bafile.

3. The apparatus of claim 2 wherein each blade has a resilient elementon its lower edge and is adapted to make continuous contact with thebaflle beneath it whenever it passes over said baffle.

4. The apparatus of claim 2 wherein the blades extend from the centralshaft outward to the walls of the vessel and extend from the top of onebaffle to the bottom of the baffle next above it.

5. The apparatus of claim 2 wherein the vessel is provided with a meansat the bottom of said vessel for collecting and settling the waxydroplets and for removing them from the bottom of the vessel.

6. The apparatus of claim 2 wherein the baffles are situated one-halfcolumn diameter apart throughout the height of the column, each bafflehaving the shape of a half disc, extending about halfway across andplaced on alternate sides of the column.

7. The apparatus of claim 6 wherein there is situated between successivebafiles, at the level of each bafile three bladed paddles, the bladesbeing apart and approximately one-half column diameter in height andattached to a central shaft so that all paddles rotate at the same time.

8. An apparatus for removing oil from partially solidified waxy oildroplets which comprises a vertical cylindrical vessel with a means atthe top of said vessel for feed ing into the vessel said waxy oildroplets, and with a means at the bottom of said vessel for feeding intothe vessel a deoiling solvent, and contained within the vesselhorizontal baflles spaced on alternate sides of said vessel throughout aportion of its height, said bafiles extending less than all the wayacross said vessel, and spaced between said horizontal bafiles, verticalpaddles which are connected to a central shaft in such a manner thatthey may rotate in a plane normal to said horizontal bafiles, saidpaddles having three blades, the outer portion of said blades beingcomprised of a resilient material which makes continuous contact withthe interior walls of said vessel and wherein the bottom portion of saidblades is comprised of a resilient material adapted to make continuouscontact with the baffle below it, the net effect of any two bladespassing over a baffle being to create a tight compartment of which thebottom portion is the baifie, one side is the interior wall of saidvessel, another side is one blade of said paddle and the last side is asecond blade of said paddle.

References Cited by the Examiner UNITED STATES PATENTS 2,029,688 2/36Wilson 196-14.52 2,029,690 2/36 Wilson 196-14.52 2,029,691 2/36 Robinson208 317 2,116,144 5/38 Dickinson 208-31 2,354,247 7/44 Dons et al 208313,083,154 3/63 Gersic et a1 208-31 FOREIGN PATENTS 808,622 2/59 GreatBritain.

841,562 7/60 Great Britain.

ALPHONSO D. SULLIVAN, Primary Examiner.

DANIEL E. WYMAN, Examiner.

1. APPARATUS FOR REMOVING OIL FROM WAXY OIL DROPLETS WHICH COMPRISES INCOMBINATION: (A) A VERTICAL CYLINDRICAL VESSEL, (B) MEANS FORINTRODUCING WAXY OIL INTO SAID VESSEL, (C) MEANS FOR INTRODUCING SOLVENTINTO SAID VESSEL, (D) A PLURALITY OF SPACED BAFFLES ON ALTERNATE SIDESOF SAID VESSEL THROUGHOUT ITS HEIGHT, SAID BAFFLES EXTENDING LESS THANALL THE WAY ACROSS SAID VESSEL, (F) A PLUALITY OF PADDLES CONNECTED TO ACENTRAL SHAFT AND LOCATED BETWEEN EACH SET OF TWO BAFFLES, SAID PADDLESHAVING THREE BLADES, THE BLADES BEING SPACED APPROXIMATELY EQUIDISTANTAPART, THE OUTER EDGE OF SAID BLADES BEING IN CONSTANT CONTACT WITH THEINTERIOR WALLS OF SAID VESSEL AND THE LOWER EDGE OF EACH BLADE BEINGLOCATED SO AS TO MAKE CONTINUOUS CONTACT WITH THE BAFFLE IMMEDIATELYBELOW IT.